Use of adjuvant chemotherapy and radiation therapy for colorectal cancer in a population-based cohort.

PURPOSE Randomized trials have demonstrated that adjuvant chemotherapy improves survival for patients with stage III colon cancer and that chemotherapy combined with radiation therapy improves survival for patients with stage II or III rectal cancer. This population-based study was designed to assess use of these treatments in clinical practice. PATIENTS AND METHODS From the California Cancer Registry, we identified all patients diagnosed during 1996 to 1997 with stage III colon cancer (n = 1,422) and stage II or III rectal cancer (n = 534) in 22 northern California counties. To supplement registry data on adjuvant therapies and ascertain reasons they were not used, we surveyed physicians or reviewed office records for 1,449 patients (74%). RESULTS Chemotherapy rates varied widely by age from 88% (age < 55 years) to 11% (age >or= 85 years), and radiation therapy varied similarly. Adjusting for demographic, clinical, and hospital characteristics, chemotherapy was used less often among older and unmarried patients, and radiation therapy was used less often among older patients, black patients, and those initially treated in low-volume hospitals. Adjusted rates of chemotherapy varied significantly (P <.01) among individual hospitals: 79% and 51%, respectively, at one SD above and below average (67%). Physicians' reasons for not providing adjuvant therapy included patient refusal (30% for chemotherapy, 22% for radiation therapy), comorbid illness (22% and 14%, respectively), or lack of clinical indication (22% and 45%, respectively). CONCLUSION Use of adjuvant therapy for colorectal cancer varies substantially by age, race, marital status, hospital volume, and individual hospital, indicating opportunities to improve care. With enhanced data on adjuvant therapies, population-based registries could become a valuable resource for monitoring the quality of cancer care.